In recent years, the popularity of the combat game known as "Paintball" or sometimes "Survival" has increased dramatically. In one form of this game, players on two teams are each supplied with a paintball gun and a number of paintballs, that is, rounds of ammunition. The paintballs comprise a spherical gelatin or similar shell filled with a non-toxic, water-soluble, biodegradable paint. Paintball guns fire these paintballs at relatively low muzzle velocity. When a competitor is hit with a paintball, the ball ruptures, "painting" the target providing dramatic evidence of the hit, without substantially injuring the competitor. Paintball games are organized on levels from local competition to international matches, and paintball outings are often set up between competing teams used for executive training and relaxation, or for military training maneuvers and the like.
Paintball guns typically fire paintballs using compressed air, CO.sub.2, or nitrogen, but pump guns, requiring the player to repressurize a chamber by hand action before each shot, are also known. The present invention is relevant to both types of paintball gun.
Several patents are directed specifically towards paintball guns. For example, Gardner U.S. Pat. No. 5,228,427 shows an improved barrel for a paintball gun wherein a number of radial holes are drilled in the paintball gun's barrel in a spiral pattern in order to cause the paintball to spin around its longitudinal axis in flight. According to the Gardner invention, the paintball would be stabilized in flight solely by imparting angular momentum to the ball about its longitudinal axis; no aerodynamic effect would be induced thereby.
U.S. Pat. No. 4,819,609 to Tippman shows an automatic feed paintball gun wherein paintballs are automatically supplied to reload the gun. U.S. Pat. No. 4,936,282 to Dobbins is generally similar.
One problem with paintball guns and ammunition as presently constituted is recognized by Gardner, that is, that the effective range of the paintball guns is very limited. Essentially this is because the paintballs are rather large projectiles, typically 0.680 calibre (although 0.620 calibre paintballs are also available), are not very dense, and are fired at low muzzle velocities, for obvious safety reasons. The effect is that a rather large amount of drag is provided in comparison to the momentum provided to the paintball upon firing.
More specifically, the common rules for paintball competition specify an initial muzzle velocity of no more than 280-300 feet per second. A typical 0.13-0.16 ounce paintball is reasonably accurate up to about 50 feet, with a maximum flight of about 150 feet. Obviously, the players in paintball games would enjoy the games more if paintballs of increased range and accuracy could be provided without substantially increasing the cost of the paintballs or without increasing the initial muzzle velocity greatly, as this would increase the danger of accidental injury.
In most cases, a smooth-surfaced paintball is fired from a smooth-bore, uniform barrel. The result is a "knuckleball"--that is, a ball without spin. A ball without spin behaves unpredictably.
As noted above, the Gardner patent teaches a barrel for a paintball drilled in a spiral pattern, to induce spin about the direction of flight. This serves to stabilize the flight, as in the case of a properly-thrown football, but does not add to the effective range of the ball.
Non-spherical paintballs, specifically, oblate spheroid "football" shaped paintballs, have also been tried, with mixed success. In any case, non-spherical paintballs are not satisfactory because they must be loaded one by one into a magazine which insures their correct orientation; this is a significant detriment. Spherical paintballs, by comparison, can simply be poured loose into a container for supply as needed.
Conventionally, paintballs are smooth surfaced. Of course, it has been well known for decades that smooth surfaces are not optimal for all projectiles. For example, golf balls are dimpled so as to increase their lift, that is, to increase the range of the golf ball's flight for a given initial velocity and trajectory. See "The Flight of the Ball: Spin, Lift, and Drag", chapter 24 of The Search for the Perfect Swing, Cochran and Stobbs (1968). This reference describes clearly the manner whereby backspin imparted to a properly struck golf ball provides lift. Any backspin reduces the effective air pressure above the ball so that it is given aerodynamic lift. The dimples of the golf ball increase friction between the surface of the ball and the air, increasing the lift accordingly.
Prior art paintballs have not been provided with dimples or the equivalent, insofar as known to the present inventors. Similarly, the prior art known fails to suggest any paintball gun effectively imparting backspin to a paintball upon firing.
U.S. Pat. No. 4,696,347 to Stolov shows an arrangement for propelling liquid-filled projectiles over long distances. For example, Stolov teaches firing water-filled projectiles over long distances to extinguish fires, irrigate remote areas, or the like. Stolov teaches that lift can be imparted to such projectiles, and therefore their range can be increased, if the surface of the projectiles is dimpled and if backspin is imparted. However, there is no suggestion that Stolov's teachings might be usefully applied to paintballs. More particularly, there is no suggestion in Stolov of anything remotely approaching a practical paintball gun. Stolov teaches a large magazine of large volume, very heavy projectiles. Backspin is imparted to these projectiles by supplying compressed air to jets located in the underside of a barrel. Stolov's teachings thus could not be applied to providing increased range to a paintball.